Error Adding Backup Drive For Windows Backup Server

This article explains options. The 3rd option is one needed if you don’t want to connect all the backup drives at once or cannot:

Add a new disk to the backup schedule by running the wbadmin command from an elevated command prompt.

Run the following command from an elevated command prompt to determine the Disk Identifier of the new disk:

wbadmin get disks

Based on the output, locate the disk that will be added to the scheduled backup. Make a note of the Disk Identifier. The output will resemble the following:
Disk name: xxxxxxxxxxx
Disk number: x
Disk identifier: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}
Total space: xxx.xx GB
Used space : xxx.xx GB
Run the following command to add the new disk to the Scheduled backup. Use the Disk Identifier from the previous step as the “AddTarget” parameter. (MAKE SURE ITS THE BACKUP DRIVE ID YOU USE AND NOT THE SOURCE)